Anthocyanins

Anthocyanins are water-soluble pigments in the flavonoid class that give red, purple, and blue colors to many fruits, vegetables, and flowers. They are glycosides of anthocyanidins; common aglycones include cyanidin, delphinidin, pelargonidin, peonidin, malvidin, and petunidin.

Anthocyanins are abundant in berries (such as blueberries, blackberries, and cranberries), grapes, red onions, red cabbage, and purple corn, among other plant tissues. Their presence helps attract pollinators and seed dispersers, while also contributing to plant stress responses.

In plants, anthocyanins are produced via the phenylpropanoid pathway from phenylalanine. Enzymes such as chalcone synthase, chalcone isomerase, flavanone 3-hydroxylase, dihydroflavonol 4-reductase, anthocyanidin synthase, and UDP-glucose: flavonoid 3-O-glucosyltransferase catalyze steps that yield various glycosylated pigments; acyltransferases add acyl groups that influence hue and stability.

The color of anthocyanins is highly pH-dependent, ranging from red in acidic conditions to blue in alkaline ones. Their hue can be altered by co-pigmentation, metal ions, temperature, and light exposure.

Anthocyanins are relatively unstable to processing and storage; heating, light, and pH changes promote degradation. Stabilization mechanisms include co-pigmentation and acylation, as well as formulation in acidic environments.

In nutrition, anthocyanins are studied for antioxidant activity and potential health benefits, but clinical evidence is inconclusive and bioavailability varies. They are widely used as natural food colorants (often labeled as E163) with regulatory status differing by country.